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Polymyositis, invasion of non-necrotic muscle fibres, and the art of repetition

BMJ 2004; 329 doi: (Published 16 December 2004) Cite this as: BMJ 2004;329:1464
  1. Gerald J D Hengstman, resident in neurology,
  2. Baziel G M van Engelen, neurologist
  1. 1 Neuromuscular Centre Nijmegen, Department of Neurology, University Medical Centre Nijmegen, PO Box 9101, 6500 HB Nijmegen, Netherlands
  1. Correspondence to: G J D Hengstman

    The presence of cellular inflammatory infiltrates with invasion of non-necrotic muscle fibres has become a prerequisite for the diagnosis of polymyositis, but a structured literature search shows that the research evidence is insufficiently strong for this histological feature to be used as a diagnostic criterion

    A dispute has erupted over the diagnostic criteria for polymyositis, a disorder characterised by progressive muscle weakness and the presence of inflammatory infiltrates in skeletal muscle tissue that could leave many myositis patients diagnostically adrift and excluded from receiving potentially effective treatment. It might also lead to the results of clinical studies performed by one specialist not being accepted by another because of disagreement over the diagnostic criteria used. The dispute focuses on the histopathological characteristics of polymyositis and whether the presence of inflammatory infiltrates invading non-necrotic muscle fibres is a prerequisite for the diagnosis.

    To examine the validity of this presumed histological characteristic of polymyositis, we traced the original source of this statement by performing a structured literature search. We subsequently studied the original source in the light of present day knowledge on myositis.

    The dispute

    The idiopathic inflammatory myopathies are a group of heterogeneous disorders characterised by acquired progressive muscle weakness and inflammatory infiltrates in skeletal muscle tissue. The three main disorders in this group are dermatomyositis, polymyositis, and inclusion body myositis. These diseases differ strongly from each other, both clinically and pathophysiologically. Dermatomyositis seems to be a humorally mediated angiopathy resulting in myositis and a typical dermatitis.1 Polymyositis is traditionally seen as an inflammatory myopathy mediated by cytotoxic T cells, which can occur in the context of another inflammatory connective tissue disease such as systemic sclerosis.1 Inclusion body myositis, which is seen mainly in elderly people and is clinically characterised by slowly progressive asymmetric muscle weakness, is thought to be a degenerative …

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